Method and device with separate emission/reception functions for making eddy current tests on an electrically conducting part

Abstract

A method for making eddy current tests on an electrically conducting part ( 13 ), in which a sensor moves above this part, uses separate emission/reception functions. The method includes obtaining a first complex voltage curve at the terminals of a reception winding ( 12 ), obtaining at least one second complex voltage curve at the terminals of a reception winding, determining at least one given distance that minimizes the modulus of the difference between the first curve and the at least one second curve, calculating the arithmetic mean (d) of the at least one given distance, choosing this arithmetic mean+/−20% as the distance between the two emission and reception windings, and detecting if one or several defects are present in this part.

1. Method with separate emission/reception functions for making eddy current tests on an electrically conducting part ( 13 ) with an electrical conductivity σ 1  and relative magnetic permeability μ r1 , in which a sensor comprising at least one assembly formed from at least one emission winding ( 11 ) emitting an electromagnetic field and at least one reception winding ( 12 ) influenced by the electromagnetic fields produced by eddy currents induced in this part ( 13 ), moves above this part, characterised in that it comprises the following steps:
 obtain a first complex voltage curve ( 20 ) at the terminals of a reception winding ( 12 ), depending on the distance between the corresponding emission winding ( 11 ) and this reception winding, for the nominal distance between the sensor and a portion of this part without any defects or another part without any defects, 
 obtain at least one second complex voltage curve ( 21 , 22 ) at the terminals of a reception winding, as a function of the distance between the corresponding emission winding and this reception winding, for at least one distance (e) different from the nominal distance between the sensor and a portion of this part with no defects or another part without any defects, 
 determine at least one given distance (di) that minimises the modulus of the difference between the first curve ( 20 ) and the at least one second curve ( 21 ,  22 ), 
 calculate the arithmetic mean (d) of the at least one given distance (di), 
 choose this arithmetic mean+/−20% as the distance between the two emission and reception windings 
 detect if one or several defects are present in this part. 
 
     
     
       2. Method according to  claim 1 , in which the electrical conductivity σ 2  in the portion of the part with no defects or in another part without any defects, is such that 0.05×σ 1 ≦σ 2 ≦20×σ 1  and the relative magnetic permeability μ r2  is such that 0.05×μ r1 ≦μ r2 ≦20×μ r1 . 
     
     
       3. Method according to  claim 1 , in which the step to obtain at least two curves is done by measurement or calculation. 
     
     
       4. Method according to  claim 1 , in which the emission and reception windings are arranged on each side of a support. 
     
     
       5. Method according to  claim 4 , in which the support is a flexible support in which the emission and reception windings are etched. 
     
     
       6. Method according to  claim 5 , in which the flexible support is a kapton film. 
     
     
       7. Method according to  claim 1 , in which the range of frequencies used is between 10 Hertz and 50 Megahertz. 
     
     
       8. Method according to  claim 1 , in which a magnetic material is placed at the centre of each winding and/or close to each winding, on the side opposite the part to be tested, so as to reduce the reluctance of the magnetic circuit in each emission winding/reception winding pair. 
     
     
       9. Device with separate emission/reception functions for making eddy current tests on an electrically conducting part, characterised in that it comprises:
 at least two rows composed of at least one element formed from at least one emission winding emitting an electromagnetic field and at least one reception winding, 
 
       and in that:
 each row is offset from the next row by a distance p, each winding of the same nature on a particular row being at a distance n×p from its closest neighbour, where n is the number of rows, 
 the distance between an emission winding and a reception winding of each element in each of the rows is equal to d+/−20%, where d is the arithmetic mean of at least one distance (di) that minimises the modulus of the difference between a complex voltage curve ( 20 ) for a nominal distance between the sensor and a portion of this part without any defects or another part without any defects, and at least one complex voltage curve ( 21 ,  22 ) for at least one distance different from the nominal distance. 
 
     
     
       10. Device according to  claim 9 , in which at least two rows are at different heights. 
     
     
       11. Device according to  claim 9 , in which the emission and reception windings are arranged on each side of a support for each row. 
     
     
       12. Device according to  claim 11 , in which an electrical insulation is arranged between two consecutive rows.